noun, plural: notches
(1) (anatomy) V-shaped cut, indentation, or nick, especially at the edge of an object or structure
(2) (developmental biology) A family of receptors, which upon binding with ligands, plays a major role in neurogenesis, specifically during lateral inhibition (wherein neuroblasts are singled-out from the neuroectoderm) and during binary cell fate specification (wherein ectodermal cells are prevented from differentiating into neuroblasts)
In developmental biology, the notch pertains to the a family of receptors (and the gene associated with their expression), which were first identified in fruit flies (Drosophila spp.). The name notch is derived from the notch that formed on the wings of fruit flies.